In a hydraulic shock absorber for a vehicle, for example, the interior of a cylinder is divided into two fluid chambers by a piston, the fluid chambers are connected by a passage penetrating the piston vertically, and a leaf valve is provided in an outlet of the passage as a damping valve. Thus, a damping force is generated in relation to displacement of the piston. The leaf valve is typically constituted by a plurality of laminated leaves, and the passage is opened when an outer peripheral portion of the leaf valve deforms in accordance with an upstream/downstream differential pressure. Accordingly, the leaf valve tends to generate excessive damping force when a displacement speed of the piston is in a medium to high speed region.
JPH09-291961A, published by the Japan Patent Office in 1997, proposes a damping valve in which an inner periphery of the leaf valve is supported elastically by a coil spring rather than being fixed, whereby a damping force characteristic of the leaf valve is improved.
Referring to FIG. 16, in a shock absorber provided with this damping valve, a tubular piston nut N is screwed to a tip end of a piston rod R penetrating a piston P. A leaf valve L serving as the damping valve opposes an outlet of a passage Po penetrating the piston P, and the leaf valve L is attached to an outer periphery of the piston nut N to be capable of displacing in an axial direction. Meanwhile, a coil spring S supported on the piston nut N at one end keeps an inner peripheral portion of the leaf valve L in elastic contact with the piston via a pressing member M attached slidably to an outer periphery of the piston nut N.
When the piston P moves upward in the figure, working oil flows through the passage Po from an oil chamber above the piston P to an oil chamber below the piston P, and a damping force is generated by a flow resistance of the leaf valve L provided at the outlet. When the piston speed is in a low speed region, an outer peripheral portion of the leaf valve L deflects downward in the figure using the inner peripheral portion, which is supported by the pressing member M, as a fulcrum. When the piston speed reaches a medium to high speed region, a pressure of the working oil passing through the passage Po exceeds an elastic force of the coil spring S, and therefore the leaf valve L displaces axially downward from the piston P together with the pressing member M. As a result, the leaf valve L opens widely, thereby ensuring that the damping force does not increase excessively. In other words, as shown in FIG. 17, the damping force increases smoothly relative to the piston speed even in the medium to high piston speed region of the piston speed.